The present invention relates to the field of elastic suspension of bed bases and seats pour sofas or armchairs. It relates especially, though not exclusively, to the elastic suspension of slats of a slat bed base.
It relates more particularly to a suspension device for a bed base or a seat, comprising:                an upper section fitted with a top plate capable of supporting a mattress;        a lower section comprising means for fixing the suspension device to the bed base or to the seat, said lower section being connected to the upper section by suspension means;        means for modifying the stiffness of the suspension device.        
Such a suspension device is especially described in document FR 2 945 195. In this document, the means for modifying the stiffness of the suspension device comprise a rigid stiffening element which lodges between either of the lower and upper sections and a spring element of the suspension device. The resulting connecting leads to increasing the stiffness of the spring element, and therefore that of the suspension device.
A drawback to this suspension device is that the presence of the stiffening element substantially decreases the deformation range of the suspension device. Substantial force is therefore necessary to deform the suspension device, which is likely to harm the impression of comfort given by the suspension device.